1. Field of the Invention
The present invention relates to a security system for monitoring theft of merchandise items placed on merchandise racks at a shop.
2. Description of the Related Art
A security system is known for monitoring theft of merchandise items for sale or display. In such a system, a sensor is attached to each merchandise item, and when detached, notifies a monitoring device of the detachment via a wire. In this case, the monitoring device gives an alarm in response to the notification from the sensor.
The monitoring device (master unit) and the sensor are generally connected by a wire. A plurality of (for example, 10) sensors are connected to one monitoring device. For this reason, for example, if the merchandise items are arranged at narrow intervals, as indicated by 14A of FIG. 14, the wiring is a nuisance. If the merchandise items are arranged at wide intervals, the wires may be short, as indicated by 14B of FIG. 14, and it may be impossible to use all sensors.
To solve this problem, a technique of eliminating the wiring is also known. PTL 1 discloses a technique of adhering a box incorporating an IC tag to each merchandise item and causing a monitoring station (master unit) incorporating a reader to always wirelessly communicate with the box (slave unit). In this technique, if no response to the polling from the monitoring station is returned from the box, the monitoring station detects the abnormality and sounds a buzzer.